1. Field of the Invention
This invention relates to a control system for a gas turbine aeroengine.
2. Description of the Related Art
Safety is the top priority in a gas turbine aeroengine. Therefore, as taught by U.S. Pat. No. 4,716,531, for example, an aeroengine is equipped with dual control channels and each control channel is provided with a monitor system. If the active control channel should fail, the other control channel takes over. This system configuration is required by aviation laws and regulations. The assignee's U.S. Pat. No. 6,353,790 teaches a similar technology.
Such control channels today utilize an electronic control unit equipped with CPUs (central processing units). In view of the extremely high reliability required, two CPUs are necessary in the fuel control channel. Moreover, still higher reliability is required of the overspeed protector (OSP), so it is ordinarily provided as a separate unit. Owing to the need for redundancy regarding the fuel control channel CPUs, the aforesaid prior art system detects CPU failure by use of a WDT (watchdog timer) circuit and is therefore not adequate regarding failure detection accuracy.
In addition, the time limited dispatch (TLD) concept was recently introduced with regard to the aeroengines on regular flight schedules. TLD specifies that an engine may be operated and used for a certain period of time despite a failure condition in a redundant component. The prior art systems have a drawback in not being thoroughly TLD compatible.